The present application is the national stage filing of and claims priority to International Application No. PCT/EP97/04008, filed Jul. 24, 1997 and Italian Application Serial No. MI96A001722, filed Aug. 7, 1996.
The present invention relates to a hydraulic binder, a dry premix, a cement composition having improved property to maintain, after the installation, for longer time periods the brilliance and the colour quantity.
One of the most important use for cement (either grey or white) is in the manufacture of the so called xe2x80x9carchitectural concretesxe2x80x9d, i.e. castings in work with not treated (flat or profiled) or treated (for example sand-blasted) surfaces. Particularly the white cement is used as a decorative element in the light prefabrication and in the production of paving tiles. The architectural concrete composition, particularly the white one, must meet the requirement to obtain besides good mechanical resistances and durability with time also surfaces having good appearance and therefore uniform in colour and texture.
In order to obtain architectural concretes having homogeneous colour and constant composition it is essential the selection of the inert material but, while said inert material forms up to 80% of the concrete mass, the concrete surface has a composition differing from the underlying layers and therefore from its whole mass: the coarse inert material does not appear on the surface and the surface itself consists only of cement paste and sand.
As a consequence a surface of concrete manufactured with white cement and light sand turns out to be good, even if the coarse aggregate is darker.
The colour uniformity of the sand is less important than in the case of grey cement architectural concrete: the colour constancy of the white cement may cover, obviously within certain limits, the colour variations of the sand.
The principal problem of architectural concrete manufactures, both in grey cement and in white cement, concerns the constant maintenance with time of the original appearance; it is important to defer as late as possible the natural ageing process due, essentially, to the influence of atmospheric agents.
The protection of these manufactures is principally carried out with water-repellent products which are applied on the surfaces by spray or brush, as for example silicone solutions, which are stable in an alkaline environment, and possibly to light and bad weather. However, perhaps owing to the progressive increase of pollutants present in a typical metropolitan environment, the superficial protection of these products resists in towns for a more and more limited time with subsequent aesthetic degradation of the manufacture. In most cases the quick aesthetic degradation of these materials prevents from using these architectural concretes.
Therefore the need is felt to solve the problem of the preservation of the original appearance of the surface of the architectural concretes for longer time periods.
The Applicant has surprisingly found that this problem may be effectively solved using hydraulic binders comprising in bulk particles of suitable photocatalysts able A oxidize in the presence of light, oxygen and water the polluting substances present in the environment.
Any kind of photocatalyst able to oxidize -n the presence of light, air and environmental humidity (oxygen and water) the polluting substances contacting the surface of the hydraulic binder (or the relative mortars and concretes) in a hardened state is part of the present invention, particularly a titanium dioxide, mainly in the form of anatase, or a precursor thereof, optionally doped with other atoms different from Ti.
The present invention further relates to a method to preserve unaltered the brilliance and the colour quantity of an installed hydraulic binder for cement compositions characterized in that particles of said photocatalyst are added to said binder before the same is installed.